Portable, handheld microanalytical systems, which have been termed “chemical laboratories on a chip,” are being developed to enable the rapid and sensitive detection of particular chemicals, including pollutants, high explosives, and chemical and biological warfare agents. These microanalytical systems should provide a high chemical selectivity to discriminate against potential background interferents and the ability to perform the chemical analysis on a short time scale with high sensitivity. In addition, low electrical power consumption is needed for prolonged field use.
Current gas-phase microanalytical systems typically comprise a gas chromatography column to separate the chemical species, or analyte, in a gas mixture and a detector to detect the separated species. Such microanalytical systems can also include a chemical preconcentrator. The chemical preconcentrator serves the important function of collecting and concentrating a chemical analyte on a sorptive material at the inlet of the microanalytical system. In particular, selective analyte preconcentration is an essential step for early-warning, trace chemical detection in real-world, high-consequence environments where a high background of potentially interfering compounds exists. The chemical preconcentrator can deliver an extremely sharp analyte plug to the downstream gas chromatograph by taking advantage of the rapid, efficient heating of the sorbed analyte with a low-heat capacity, low-loss microhotplate. The very narrow temporal plug improves separations, and therefore the signal-to-noise ratio and detectability of the particular chemical species of interest.
Previous microfabricated chemical preconcentrators have used a heated planar membrane suspended from a substrate as the microhotplate, wherein the sorptive material is disposed as a layer on a surface of the membrane to sorb the chemical species from a gas stream. See U.S. Pat. No. 6,171,378 to Manginell et al., which is incorporated herein by reference. The high thermal efficiency and extremely low heat capacity of the planar preconcentrator enables rapid thermal desorption of the chemical analyte with very low power consumption. However, analyte uptake on the sorptive layer is not optimum, due to sorptive materials limitations and the low collection area of the sorptive layer of the planar preconcentrator. Additionally, to allow for adequate contact of the analyte with the sorptive layer, intricate, post-process manifolds and/or flow lids may be required. Finally, the rapid desorption of the analyte when heated may cause the flow chamber to overpressure and rupture the thin suspended membrane, destroying the planar preconcentrator.
The present invention directly addresses the problems described above. Like the planar preconcentrator, the microscale non-planar chemical preconcentrator of the present invention can have a high thermal efficiency and a low heat capacity, enabling rapid desorption of the sorbed chemical analyte with low power consumption. However, the non-planar chemical preconcentrator uses a high-surface area, low mass, three-dimensional, flow-through support structure that can be coated or packed with a sorptive material. The high-surface area of the sorption support structure allows improved analyte collection and concentration, especially important for trace chemical detection. Furthermore, the flow-through structure allows pressure equalization across the thin heated membrane, preventing membrane rupture due to overpressure from analyte desorption and improving the mechanical ruggedness of the device. The non-planar chemical preconcentrator can be easily integrated with other microanalytical system components in a hybrid or monolithic fashion.